The present invention relates to a rotary connector used for the steering device of an automobile. More specifically, it relates to a rotary connector which establishes electric connections between an electric circuit secured to the steering column and an electric circuit attached on the steering wheel to be rotated, using a flexible flat cable.
Conventionally, such a rotary connector described above, is made of following components:
(a) an outer case fixed to the steering column of an automobile;
(b) an inner case attached to the steering wheel shaft rotating with the steering wheel; and
(c) a flat cable for establishing electric connections between the outer case side and the inner case side.
Such rotary connectors are broadly categorized into two types in terms of the winding way of the flat cable:
1. the winding that is spiral in one direction between the outer case and the inner case;
2. the winding that is reversed in direction at a midpoint of the flat cable.
Comparing two rotary connectors having a same outside dimension in which the flat cable is wound according to the two ways, the xe2x80x9creversedxe2x80x9d winding can save the length of the flat cable, with reduced parts cost. The rotary connector with the xe2x80x9creversedxe2x80x9d winding has therefore been popular in recent years.
Now will be explained about conventional rotary connectors with the flat cable spirally wound in one direction, referring to FIGS. 9 to 12.
FIG. 9 is a cross-sectional view and FIG. 10 is an exploded perspective view of a conventional rotary connector. The conventional rotary connector, as shown in FIGS. 9 and 10, comprises following components:
(a) cylindrical outer case 1 with the top and bottom surfaces open;
(b) inner case 2 accommodated in outer case 1 rotatably relative to outer case 1;
(c) cover 3 which is fixed to outer case 1 to cover the opening at the bottom of outer case 1; and
(d) flexible flat cable 5 which is housed in ring-shaped space 4 between outer case 1 and inner case 2.
Inner case 2 is made of lid 2A which covers the top opening of outer case 1, and inner cylinder 2B having shaft hole 2C which protrudes downwardly from the center of the rear surface of lid 2A.
Ring-shaped space 4 is formed between inner wall 1A of outer case 1 and inner cylinder 2B of inner case 2. Wound in several turns, flat cable 5 is accommodated in space 4. Flexible flat cable 5 has band-shaped appearance, covering a plurality of conductive wires together. The inside end of flat cable 5 is connected to terminal 5A that is secured to inner case 2. Terminal 5A is further connected to inner connector 6. On the other hand, the outside end of flat cable 5 is connected to outer connector 7, which is fixed to outer case 1 and coupled to an external electric circuit.
In addition, elastic tongue-shaped piece 8, such as an insulating sheet, is attached to the inside end of flat cable 5. The end of tongue-shaped piece 8 is inserted in terminal 5A and is secured. A conventional rotary connector has such constitution described above. Outer case 1 of the rotary connector is fixed to a steering column (not shown) of an automobile. The steering wheel shaft (not shown) is inserted into shaft hole 2C of inner cylinder 2B of inner case 2. Formed in such structure described above, a conventional rotary connector is attached to the steering device of an automobile.
Outer connector 7, which is secured to outer case 1, is coupled to an electric circuit fixed to the steering column on the car body side. On the other hand, inner connector 6, which is secured to inner case 2, is coupled to an electric circuit within the steering wheel. In this manner, the electric connection between the steering wheel and the steering column is established via flat cable 5.
Now will be described how the rotation of steering wheel effects the winding state of flat cable 5 in the conventional rotary connector structured above.
FIG. 9 shows the state of flat cable 5 being wound evenly on the side of inner wall 1A of outer case 1 and the side of inner cylinder 2B of inner case 2. In this state, the steering wheel is held at a neutral position. Rotating the steering wheel from the neutral position rotates inner case 2 attached to the steering wheel shaft.
When the steering wheel is rotated in a clockwise direction, flat cable 5, shown in the cross-sectional view of FIG. 11, is wound on the side of inner cylinder 2B of inner case 2. In this case, flat cable 5 is wound more on the side of inner cylinder 2B than the side of inner wall 1A of outer case 1.
On the other hand, when the steering wheel is rotated, from the state shown in FIG. 9, in a counterclockwise direction, flat cable 5 is now wound more on the side of inner wall 1A, as shown in the cross-sectional view of FIG. 12. At this time, the inside end of flat cable 5 is guided by tongue-shaped piece 8. This protects flat cable 5 from buckling or deformation indicated by the broken line in FIG. 12.
As described above, the conventional rotary connector employs tongue-shaped piece 8 to prevent the inside end of flat cable 5 from buckling or deformation when the steering wheel is rotated in a counterclockwise direction. This, however, inconveniently not only increases the number of parts of the rotary connector but also consumes the time for assembling.
The present invention addresses the problems discussed above and aims to provide an economical and easy to assemble rotary connector with minimized number of parts.
To achieve the object described above, the rotary connector of the present invention comprises:
(a) a cylindrical outer case with the top and bottom surfaces open;
(b) an inner case accommodated in the outer case rotatably relative to the outer case, having a lid covering the top opening of the outer case and also having an inner cylinder protruding downwardly from the center of the rear surface of the lid;
(c) a cover fixed to the outer case covering the bottom opening of the outer case;
(d) a flexible flat cable housed in a ring-shaped space, with its inner and outside ends secured to inner and outer cases, respectively;
(e) a recess formed closely to where the inside end is fixed on the inner cylinder of the inner case;
(f) a guide piece formed at the recess so as to fit along the periphery of the inner cylinder, having its one end formed in one piece with the bottom surface of the lid of the inner case,; and
(g) a gap formed between the inner wall of the guide piece and the periphery of the recess on the inner cylinder.
On the tip of the guide piece described above, an edge portion is formed so as to tilt in the direction of the periphery of the inner cylinder.
Besides, a portion adjacent to the inside end of the flat cable is passed through the gap, which is formed between the inner wall of the guide piece and the periphery of the recess on the inner cylinder. The flat cable is then guided out from the tilted edge portion of the guide piece. This guiding makes the flat cable abut against an R-shaped edge surface of the tilted edge portion of the guide piece when the flat cable is rewound. With slightly warped, the flat cable is unreeled from the side of the inner cylinder. The structure described above therefore not only protects the flat cable from buckling or deformation, but also minimizes the number of parts. It is thus possible to obtain an easy to assemble rotary connector with a low cost.
As a preferred embodiment, the rotary connector according to the present invention may employ a flat cable having an U-shaped reversed portion so that the winding of the flat cable on the side of the inner wall of the outer case is opposite in direction, via the reversed portion, to the winding on the side of the inner cylinder of the inner case. To be precise, a guide-ring having a guide-gap through which a reversed portion of the flat cable passes is accommodated, as well as the flat cable, in the ring-shaped space formed between the outer and inner cases such that the guide piece is rotatably relative to the outer case. The guide-ring reverses the winding direction of the flat cable in the space between the outer and inner cases, saving the length of the flat cable. It is thus possible to provide a cost-saved rotary connector.
Rotary Connector